The present invention is directed to a device for distance measurement and/or a method for distance measurement.
Distance measurement devices and, in particular, optical distance measurement devices as such have been known for some time. These devices emit a modulated measuring beam, e.g., a light or laser beam, which is directed to a desired target object, the distance of which to the device is to be determined. A portion of the returning measurement signal that is reflected or scattered by the sighted target object is detected again by the device and used to determine the sought-after distance.
A distinction is made hereby between “phase measurement methods” and pure “transit time methods” for determining the sought-after distance to the target object. With the transmit time method, a light pulse having the shortest possible pulse duration is emitted by the measurement device, then its transit time to the target object and back to the measurement device is determined, for instance. Based on this, the distance of the measurement device to the target object can be calculated, with reference to the known value for the speed of light.
With the phase measurement method, in contrast, the variation of the phase of the measurement signal with the path that was covered is used to determine the distance between the measurement device and the target object. Based on the magnitude of the phase displacement of the returning light in comparison to the emitted light, the path covered by the light and, therefore, the distance of the measurement device to the target object can be determined.
The field of application of distance measurement devices of this type generally includes distances in the range of a few millimeters up to many hundred meters. Depending on the paths to be measured, the environmental conditions and the reflectance of the selected target object, different requirements on the performance of a measurement device of this type result. Measurement devices of this type are now available commercially in compact designs; they enable simple, handheld operation for the user.
Laser distance measurement devices are known that have a defined measurement accuracy that is defined essentially by the measurement system on which the measurement device is based. This accuracy of the distance measurement device is guaranteed for a specified measurement range of the measurement device, by the manufacturer, for instance.
A circuit arrangement and a method for optical distance measurement is known from DE 198 11 550 A1, for example, with which at least two different, closely adjacent measurement frequencies are derived from an oscillator. To permit measurement over the greatest possible measurement range and, simultaneously, to obtain the highest possible measurement accuracy in the distance measurement, three different frequencies in the range from approximately 1 MHz to approximately 300 MHz are used in the method according to DE 198 11 550 A1, and the sought-after path is measured with each of these frequencies.
An optical method for measuring distances according to the pulse transit time method is known from EP 0 885 3999 B1, with which a rough measurement procedure and a fine measurement procedure are carried out. Using a rough measurement procedure, a measurement time interval is determined that is greater than an estimated propagation time of the light signal to and from the desired target object. An appropriate measurement time range is fixed in advance within this measurement time interval. A series of sub-measurements is then carried out during the fine measurement procedure, whereby, for each sub-measurement, a measurement light signal is sent to the target object and the received, returned light pulse that is reflected by the target object is collected only within the appropriate measurement time range that was fixed during the rough measurement procedure. The exact distance of the measurement device to the target object is then determined by calculating the mean of the individual measurements in the fine measurement procedure.
The object of the present invention is to expand, using simple means, the distance range—that is, the distance range across which a distance measurement can be carried out with the device—that is usable with a compact, and, in particular, handheld measurement device for distance measurement.
This object is attained via a device for distance measurement according to the invention and via a method for distance measurement.